Niantic has recently decided to yet again make changes to the Pokemon Go egg pool; removing less desirable pokemon in order to make hatching eggs more rewarding. In the past, Niantic removed both Pidgey and Rattatta from the egg pool, becuase, well, who wants to walk 5km to get a low tier pokemon from an egg?
Anyway, Niantic has recently removed 6 more Pokemon from the egg pool as part of their latest update. Psyduck, Tentacool, Wooper, Natu, Sandshrew, and Paras will no longer be atainable through eggs. Along with removing certain Pokemon from the egg pool, Niantic also made certain Pokemon harder to receive through eggs. Dratini and Pineco will now be twice as hard to obtain from 10km eggs.
Although it is harder to receive those two pokemon from 10km eggs, at least you don’t have to worry about getting as many lower tier Pokemon anymore.